Large buildings such as office and industrial buildings and high apartment houses are nowadays constructed of reinforced concrete. Concrete roofs are cast together with the load-carrying walls into a continuous system of outwards open room-forming cells constituting a load-carrying building construction. Non-load-carrying partition walls of prefabricated elements or light bricks are built-in as planned between the load-carrying concrete walls. Finally, the building construction is terminated with a facade of prefabricated facade elements. The modern building technology has been aimed at a mechanized materials handling where the mast crane is of dominant importance. The concrete casting technique has been directed to the use of finished form elements which can be used several times for the casting of walls and roofs.
Cross-reinforced roofs or archs are cast one floor after the other according as the casting of the walls has been completed. For the casting use is made of a form table or centering consisting of a rectangular steel construction with two longitudinal beams having a pluarlity of cross beams welded thereto at equal spaces, for example 600 mm, to support a fiberboard or metal sheet onto which the roof will be cast. The centering is supported by a framework supported by a plurality of wheeled legs so that the framework may be moved in position. Furthermore, the legs are provided with screw spindles by means of which the framework may be lifted until the wheels get clear and the entire framework rests steady on the floor.
The width of the centering is governed by the space between the walls, and its length may be changed according to need. Generally, a length of, for example, 4-6 meters is chosen, and two or more centerings may be jointed with the short sides and the ends of the longitudinal beams abutting each other.
In the course of mounting for casting, the centering is hoisted by means of a fork-lift operated by the crane operator and lifted in place between the newly cast walls of the building, levelled into the desired ceiling height and sealed against the walls by means of suitable packing means. After armouring, casting the concrete mass and hardening thereof, the packing means are removed and the framework with the centering resting thereon is lowered on to its wheels and removed.
The concrete casting technique briefly described herein implies a substantial rationalization with resulting cost savings and has come into common practice. Nevertheless, it suffers from serious drawbacks. Frequently, the centerings consist of all-welded constructions which are sold or leased by the manufacturer to the building contractors. However, almost invariably there is a need of centerings with different widths for various building projects. By way of example, in one case the width may be 3.36 m, in another case 3.60 m. If only 3.60 m wide centerings are available at the site and there would be a need of 3.36 m wide centerings, it therefore often happens that all cross beams are cut down to 3.36 m by means of a cutting torch. Each time such a centering has been cut down, its cross beams must be lengthened with joint pieces or further cut down to meet the actual need. This work is very cumbrous and the costs involved have been estimated amounting approximately to half the costs of a new centering. Moreover, there will arise a large wastage of material resulting in further increased costs.